The present invention relates generally to laser-based position sensing systems useful in construction applications and, more particularly, to a method and system for determining the position of a retroreflective element in a predetermined frame of reference and for providing this position to a position sensing system for use in subsequently determining the position of any point in the predetermined frame of reference.
In the construction industry, the level of automation and robotization continues to remain very low. A significant reason for this is the difficulty of properly positioning machines and tools. In the construction of commercial buildings, for example, various points of reference have to be established, such as placement of floors, ceilings, electrical wiring, plumbing, and heating and cooling ducts. Establishing reference points is time consuming and expensive, particularly as such work is often contracted out to companies which specialize in this work.
Various laser-based position sensing systems are known which continually track the position of a reference point in a predetermined frame of reference. For example, commonly assigned U.S. Pat. No. 5,076,690 discloses a position sensing system which calculates the X-Y coordinates of a point using triangulation and determines the direction in which the point is moving. The triangulation calculation is based on the known coordinates of at least three retroreflective elements spaced apart from each other around the periphery of a two-dimensional coordinate frame, and the measured angles between the lines projected radially outward from the point to each of the retroreflective elements. The accuracy of the measured angles is achieved by using a rotating member supported by dedicated hardware and controlled by software. The member rotates with a beam of light generated by a light transmitting and detecting device positionable at the point. The light transmitting and detecting device receives the beam of light reflected back from the retroreflective elements and generates an output signal in response thereto. A computer processes the output signals for use in calculating the X-Y position of the point and the orientation of the light transmitting and detecting device when it is positioned at the point.
The precision of a position sensing system as just described is highly dependent on the ability of the operator to measure the coordinates of the three retroreflective elements accurately . Moreover, each of the respective coordinates of the retroreflective elements must be measured and entered into the computer of the system. Miscalculation of, or errors in entering, the positions of the retroreflective elements could result in time consuming and expensive removal and repositioning of various building fixtures, such as walls, plumbing and heating and cooling ducts.
Consequently, in view of the shortcomings of the above laser-based position sensing system, there is a need for a method and system for easily and accurately determining the position coordinates of the retroreflective elements while concomitantly reducing the likelihood of operator error.